The present invention relates to the general field of sound attenuation panels. More particularly, it relates to sound attenuation panels used for reducing the noise produced by aeroengines such as gas turbines or their exhausts.
In order to reduce noise in the exhaust ducts of gas turbines, it is known to provide the surfaces of elements defining such ducts with sound attenuation panels. Those panels are typically constituted by a wall having a multiply-perforated surface that is permeable to the soundwaves it is desired to attenuate, and by a reflecting solid wall, with a cellular structure, such as a honeycomb or a porous structure, being arranged between those two walls. In well-known manner, such panels form Helmholtz type resonators that serve to attenuate a certain frequency range of the soundwaves produced in the duct.
The component elements of that type of panel (walls and cellular body) are generally made out of metal material, as described in Documents U.S. Pat. No. 5,912,442 and GB 2 314 526. Nevertheless, in technical fields where saving weight is a constant concern, such as in aviation, the use of sound attenuation panels made of metal material is relatively penalizing.
Document U.S. Pat. No. 8,043,690 describes a sound attenuation panel having its walls and its cellular body made from composite materials (fiber reinforcement densified by a matrix), thereby achieving weight savings compared with the metal materials conventionally used. Nevertheless, that document discloses only panels or panel subassemblies that are plane in shape, so that providing a part of cylindrical or frustoconical shape with acoustic treatment requires a plurality of sound attenuation subassemblies that are of plane or rectilinear shape to be arranged on the wall of the part. That fabrication technique requires a large number of operations to make the acoustic panel from plane subassemblies, thereby penalizing the optimization and the costs involved in fabricating the panel.
There exists a need to have a solution enabling sound attenuation panels to be made out of composite material, and in particular out of ceramic matrix composite (CMC) material, and that presents a shape that is curved, matching the shape of the part that is to be sound proofed.